The present disclosure relates to an electric vehicle, and more particularly, to a method for preventing overheating of a traction motor in an electric vehicle, which determines driving conditions of the traction motor in consideration of a temperature, magnitude of a load, a time for which a load is applied, and a variation in temperature to prevent the traction motor from being overheated.
Eco-friendly vehicles include pure electric vehicles and fuel-electric vehicles.
Such a fuel-electric vehicle represents a vehicle driven by efficiently combining two kinds of power sources different from each other, i.e., a vehicle driven by an engine that obtains a rotation force by burning a fuel (a fossil fuel such as gasoline) and a traction motor that obtains a rotation force by using a battery power.
Such an eco-friendly vehicle adopts a traction motor as a power source. Also, the eco-friendly vehicle is designed as a future vehicle that promotes reduction of exhaust gases and improvement of fuel efficiency. Thus, studies for improving fuel efficiency and developing eco-friendly products are being actively progressed to promptly meet the needs of the times.
However, in the eco-friendly vehicle using the traction motor as described above, overheating of the motor of which a temperature increases above a predetermined level during the driving of the motor may occur.
A driving section of the motor may be divided into a maximum instantaneous rated section and a continuous rated section. Since cooling capacity is greater than a heat generation rate below the continuous rating, the motor may continuously operate without increasing in temperature. However, when the motor operates for a long time above the continuous rating, the motor may increase in temperature.
When the temperature of the motor is identified in real time to increase above a predetermined level so as to prevent the motor from being overheated, technologies for restricting an operation of the motor in the driving section to prevent a system from being damaged due to the overheating are being applied.
That is, when the temperature of the motor exceeds a critical point, maximum torque may gradually decrease to enter into a derating section in which a rated output decreases. Since the driving amount of motor is significantly reduced in the state of entering into the derating section, an additional temperature rise may be prevented.
FIGS. 1 and 2 are line graphs illustrating a torque limitation in a derating section in which maximum torque gradually decreases when exceeding a critical temperature according to a related art.
Referring to FIG. 1, output torque of a motor is controlled according to a normal maximum torque value in a normal operation section in which a temperature of the motor is below a critical point. However, the maximum torque of the motor is set to gradually decrease in a derating section in which the temperature of the motor exceeds the critical point, thereby restricting a driving amount of motor.
Also, when the maximum torque of the motor decreases, a usable driving section of the motor may change to significantly reduce power performance of the vehicle. As a result, this may cause dissatisfaction of a driver.
Thus, in recent years, a derating method in which a motor protection critical temperature is additionally set, a driving amount of motor is reduced within a range in which power performance of the vehicle is not reduced above the motor protection critical temperature and below a critical temperature to prevent the motor from being overheated is used as illustrated in FIG. 2.
However, a temperature sensor of the traction motor is attached to a specific position of the traction motor. Here, a predetermined time is taken for completely transferring heat of the traction motor to the temperature sensor.
Thus, it is difficult to identify the overheated state of the traction motor by using only the temperature of the traction motor.    (Patent Document 1) KR2008-0026609 A